The present invention relates to a cooling water flow control system for an internal combustion engine used for the control of radiator flow rate and bypass flow rate for the purpose of controlling engine temperature. In an internal combustion engine used in automobile, it is designed in such manner that cooling water does not flow to radiator during warming-up operation (in fact, cooling water is passed at very low flow rate to a bypass passage in order not to increase the load of water pump), and overheating is prevented by passing the cooling water to the radiator after the warming-up operation has been completed. During light load operation, the quantity of circulating water to the radiator is relatively reduced, and a target cooling water temperature is set to a relatively high level and this is to decrease heat loss (to improve combustion efficiency), to promote purification of exhaust gas, and to decrease friction loss in the engine. Also, during total load operation, the quantity of circulating water to the radiator is relatively increased and the target cooling water temperature is set to a relatively low level in order to improve suction air filling efficiency and to prevent knocking. For the water temperature control as described above, water jacket of engine is connected to the radiator via a radiator passage. The flow control valve is provided at a junction of a bypass passage (used to bypass the radiator) and the radiator passage, and radiator flow rate and bypass flow rate are controlled by the flow control valve. (For instance, see JP-A-2-125910).
In the conventional technique, radiator passage is closed during the warming-up operation, and the quantity of the cooling water in the bypass passage is decreased to promote the warming-up operation, but considerable time is required for the warming-up operation. Also, when it is shifted from light load operation to total load operation, the temperature is immediately controlled to the target water temperature suitable for total load operation. In this respect, when it is shifted to light load operation immediately after it has been shifted to total load operation, the response to the light load operation may be delayed, and hunting in water temperature control may occur.
It is a first object of the present invention to promote the warming-up operation in a cooling water flow control system of an internal combustion engine. It is a second object of the invention to prevent response delay or hunting in water temperature control when it is shifted to light load operation immediately after it has been shifted from light load operation to total load operation. It is a third object of the invention to accelerate control operation after it has been shifted from total load operation to light load operation or from light load operation to total load operation.
A first aspect of the present invention provides a cooling water flow control system in an internal combustion engine, which comprises a flow control valve at a junction of a radiator passage and a bypass passage, said flow control system being used for control of radiator flow rate and bypass flow rate of the flow control valve by detecting engine outlet water temperature, radiator outlet temperature, number of revolutions of engine, and suction pipe negative pressure, whereby cooling water in the bypass passage passes through a throttle body, and flow rate is set to totally closed flow rate or micro-flow rate during the warming-up operation.
A second aspect of the present invention provides a cooling water flow control system according to the first aspect of the invention, wherein, when it is shifted from light load operation to total load operation, radiator flow rate and bypass flow rate are maintained at current values for a predetermined time, radiator flow rate and bypass flow rate are calculated from number of revolutions of engine and suction pipe negative pressure after the predetermined time, a correction value is calculated from engine outlet water temperature and radiator outlet water temperature, the flow control valve is quickly controlled to adjust the corrected radiator flow rate and bypass flow rate and is maintained at its position, and feedback control of water temperature is performed after the cooling water temperature has reached xe2x80x9ctarget water temperature xc2x1 preset temperaturexe2x80x9d.
A third aspect of the present invention provides a cooling water flow control system according to the first and the second aspects of the invention, wherein, when it is shifted from total load operation to light load operation, radiator flow rate and bypass flow rate are calculated from number of revolutions of engine and suction pipe negative pressure, a correction value is calculated from engine outlet water temperature and radiator outlet water temperature, the flow control valve is quickly controlled to adjust to the corrected radiator flow rate and bypass flow rate and it is maintained at its position, and feedback control of water temperature is performed after the cooling water temperature has reached xe2x80x9ctarget water temperature xc2x1 preset temperaturexe2x80x9d.
According to the first aspect of the present invention, bypass flow rate is controlled to totally-closed flow rate or micro-flow rate during the warming-up operation. As a result, the cooling due to suction air flowing in the throttle body of the bypass passage is prevented, and this contributes to the promotion of the warming-up operation and the warming-up operation can be achieved at earlier time.
According to the second aspect of the present invention, when it is shifted from light load operation to total load operation, radiator flow rate and bypass flow rate are maintained to current values for a predetermined time. As a result, even when it is shifted to light load operation immediately after the shifting from light load operation to total load operation, response delay or hunting in water temperature control does not occur.
According to the second aspect and the third aspect of the present invention, after it is shifted from total load, operation to light load operation or from light load operation to total load operation, radiator flow rate and bypass flow rate are calculated from number of revolutions of engine and suction pipe negative pressure. A correction value is calculated from engine outlet water temperature and radiator outlet water temperature. The flow control valve is quickly controlled to adjust to the corrected radiator flow rate and the corrected bypass flow rate, and the valve is maintained at its position. After the cooling water temperature reaches the level of xe2x80x9ctarget water temperature xc2x1 preset temperaturexe2x80x9d, feedback control of water temperature is performed. Therefore, control operation after the shifting is accelerated, and cooling water temperature reaches the target water temperature at earlier time.